1. Field of the Invention
The present invention relates to computer interface control circuitry. More specifically, the present invention relates to methods and apparatus for providing a high speed, programmable interface circuit for use with computers or other data or signal processing equipment.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Computer interface control circuits are utilized to connect an external peripheral device such as a tape drive, disk drive, sensor device or the like to the internal circuitry of signal or data processing equipment. External peripheral devices often communicate with the signal and data processing equipment in accordance with different protocols (e.g., data formats, signal levels, framing of words, timing of bits, etc.). Further, signal and data processing equipment often support multiple external devices. Therefore, a computer interface control circuit often must be reconfigured for each external device that it is connected to. The interface often also utilizes a different protocol from that used by the interfaced circuits.
Conventional computer interface control circuits are typically implemented with either a hardwired logic interface, a PROM based state machine interface or a microprocessor controlled interface. A hardwired logic interface is a special purpose, dedicated interface circuit that typically exhibits a fast data rate. However, a major disadvantage of the hardwired logic interface is that it is not reconfigurable. The hardwired logic interface enables communication between the processing equipment and a particular external device. However, it cannot be easily modified to permit communication between the processing equipment and another external peripheral device without time consuming physical circuit changes. The hardwired logic interface requires a different hardware logic design for each change to the interface protocol.
The PROM based state machine interface is also designed to operate with a particular external peripheral device. The PROM based interface has the disadvantage of requiring that the PROM be reprogrammed or replaced in order to reconfigure the interface to support a different external device. This requirement results in substantial downtime of the external device and hardware changes to the interface. Therefore, when utilizing the PROM based interface, a separate PROM based circuit is required for each external device that the interface supports. The microprocessor controlled interface is easily reconfigurable while in the circuit between the signal processing equipment and the external device. However, a dedicated microprocessor is required. Although the dedicated microprocessor is typically fast, the execution of multiple instructions for each interface control activity results in a slow interface relative to the system clock speed. Therefore, the microprocessor controlled interface does not support high data rates.
The main disadvantages associated with reconfiguring conventional computer interface control circuits to connect various external devices to the signal or data processing equipment include major hardware modifications, excessive time to complete modifications and slow operating speed (e.g., low data rates). A computer interface control circuit is not available that is easily reconfigurable while in circuit for connecting a plurality of external devices to the signal or data processing equipment that can adapt to a variety of interface protocols, is autonomous of a host computer and provides a high rate of data transfer.
Thus, there is a need in the art for improvements in the design of computer interface control circuits to ensure autonomous operation and rapid and convenient reconfigurability of the interface circuit used to connect a variety of external devices to signal or data processing equipment.